This invention relates to the field of electronic displays, and, more particularly, field emission display ("FED") devices.
As technology for producing small, portable electronic devices progresses, so does the need for electronic displays which are small, provide good resolution, and consume small amounts of power in order to provide extended battery operation. Past displays have been constructed based upon cathode ray tube ("CRT") or liquid crystal display ("LCD") technology. However, neither of these technologies is perfectly suited to the demands of current electronic devices.
CRT's have excellent display characteristics, such as, color, brightness, contrast and resolution. However, they are also large, bulky and consume power at rates which are incompatible with extended battery operation of current portable computers.
LCD displays consume relatively little power and are small in size. However, by comparison with CRT technology, they provide poor contrast, and only limited ranges of viewing angles are possible. Further, color versions of LCDs also tend to consume power at a rate which is incompatible with extended battery operation.
As a result of the above described deficiencies of CRT and LCD technology, efforts are underway to develop new types of electronic displays for the latest electronic devices. One technology currently being developed is known as "field emission display technology." The basic construction of a field emission display, or ("FED") is shown in FIG. 1. As seen in the figure, a field emission display comprises a face plate 100 with a transparent conductor 102 formed thereon. Phosphor dots 112 are then formed on the transparent conductor 102. The face plate 100 of the FED is separated from a baseplate 114 by a spacer 104. The spacers serve to prevent the baseplate from being pushed into contact with the faceplate by atmospheric pressure when the space between the baseplate and the faceplate is evacuated. A plurality of emitters 106 are formed on the baseplate. The emitters 106 are constructed by thin film processes common to the semi-conductor industry. Millions of emitters 106 are formed on the baseplate 114 to provide a spatially uniform source of electrons.
However, it has been difficult in the past to make a field emission display with the required mechanical strength for a suitable commercial device. Some of the problems that have been encountered are described with respect to FIG. 2. As shown, the field emission display comprises a glass substrate 200 having a rail, or spacer, 204 provided with conductors 208 for connecting a die, or cathode 202 to a bonding wire 210 which in turn is connected to conductor 212 located on the glass substrate 200. Collectively, these parts are referred to as the "die assembly." The die assembly is then connected to the backplate assembly, comprising the backplate 200 bonded to a seal ring 216 by frit material 218. The die assembly is joined to the backplate assembly by frit material 214 and then the space between the die assembly and the backplate assembly is evacuated. However, as seen in the figure, die 202 is attached to the rail 204 only by its electrical connection with rail conductors 208. This connection typically employs flip chip bonding. The bond between die 202 and rail 204 is fragile and is subject to separation when the space between the die assembly and the backplate assembly is evacuated or when the device is subject to a mechanical impact, for example being dropped. Clearly, when the die 202 is separated from the rail 204, the device it is completely destroyed.
It has been reported that the above-mentioned problem could be addressed by placing the backplate 220 in contact with the die 202 or another member of the die assembly, such as getter 206, which is connected to the die 202. However, such a device is difficult to manufacture and would have the effect of placing two relatively flat substrates in contact with each other, raising the possibility that pockets of contaminants would be created when the space between the die assembly and the backplate assembly is evacuated.
It has also been reported that, in another attempt to solve the above-mentioned problem, a support member, or stand-off (not shown) is placed between the backplate 220 and the die 202, or getter 206. However, such a device is difficult to manufacture. For example, frit layer 214 is used to join the die assembly to the backplate assembly. When the assemblies are joined, the frit layer 214 is heated and the assemblies are pressed against each other, thus compressing frit layer 214. Therefore, it is important that the support member be precisely machined to fit the space between the die assembly and the backplate assembly, taking into account the compression of frit layer 214. If the support member (not shown) is improperly machined, it will either prevent the die assembly from sufficiently compressing frit layer 214, or it will leave a gap between the die assembly and the backplate assembly and, thus, fail to provide the proper support. Moreover, the support also prevents deflection of glass due to vacuum when sealed.
Accordingly, there is a need in the art for a field emission display having a support member which will overcome the above-mentioned problems.